This invention relates to an input level adjusting circuit in a source switching section of a control amplifier or other devices performing switching between plural audio sources and, more particularly, to an input level adjusting circuit capable of automatically adjusting signal levels which differ from one another depending upon input sources by employing a common level adjusting means thereby obviating the necessity for making tone volume adjustment each time the input source is switched.
There is a difference in the level of an output signal between different audio input source devices. In switching the audio input source device in a device such as a control amplifier, a master volume of the device must be adjusted each time such switching is made.
For eliminating this inconvenience, there has been proposed an input level adjusting device in which the amount of adjustment of tone volume is preset for each source in a device such as a control amplifier and, therefore, there does not occur change in the tone volume when the input source has been changed.
In this prior art device, as shown in FIG. 17, level adjusting volumes 2a through 2d are provided for source input terminals 1a through 1d and one of source signals which have been adjusted in the tone volume by the level adjusting volumes 2a through 2d is selected by an input selector 3 and supplied to a post stage circuit.
This prior art input level adjusting device requires a plurality of level adjusting volumes 2a through 2d and these volumes 2a through 2d are normally disposed on the back side of the control amplifier or the like device with resulting difficulty in adjusting these volumes 2a through 2d. Besides, the number of volumes must be increased in proportion to increase in the number of input sources.
It is, therefore, an object of the invention to provide an improved input level adusting circuit which is of a simpler construction.